Method and apparatus for real time testing of DTV antenna transmitting systems in time domain under full power

ABSTRACT

A real time apparatus for testing a DTV antenna transmitting system, wherein the DTV antenna transmitting system transmits an original signal from a DTV transmitter to a DTV transmitting antenna, is disclosed that includes a probe, wherein the probe is connected in series with the DTV antenna transmitting system, and senses signals traversing the DTV antenna transmitting system. An error detector of the testing apparatus compares the received signal to the original signal to identify the magnitude and location of errors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and is a continuation of U.S. patent application entitled, METHOD AND APPARATUS FOR REAL TIME TESTING OF DTV ANTENNA TRANSMITTING SYSTEMS IN TIME DOMAIN UNDER FULL POWER, filed Apr. 5, 2002, having a Ser. No. 10/116,112, now U.S. Pat. No. 7,015,948, the disclosure of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to an antenna testing system. More particularly, the present invention is directed to a method and apparatus for real time testing of digital television (DTV) antenna transmitting systems.

BACKGROUND OF THE INVENTION

The Federal Communications Commission has required television broadcasters to transition from their current National Television System Committee (NTSC) analog antenna systems to DTV antenna systems. DTV technology allows for the transmission of television programming having higher resolution pictures and better sound quality than NTSC analog antenna systems. DTV systems also allow broadcasters to transmit more than one signal per channel, and thus, deliver more than one television program per station.

Test receivers exist for identifying problems in the transmission of a DTV signal from the DTV transmitting antenna to a particular point of reception, but problems can also occur in the transmission of the DTV signal from a DTV transmitter to the DTV transmitting antenna that prevent a signal generated by the DTV transmitter from reaching the DTV transmitting antenna.

Echoes are reflected signals that occur when the impedance is not properly matched between components of the DTV transmitting system and can be an indicator of potential problems in the transmission of a DTV signal. The echo/reflected signals “add to” or “subtract from” the signal being transmitted from the DTV transmitter to the DTV transmitting antenna, and, as such, increase or decrease the level of the DTV signal. Although echoes commonly occur during the transmission of a DTV signal, they will cause problems if their magnitude increases to a level that interferes with the transmission of the DTV signal.

When echo levels exceed an acceptable threshold, the signal received by the transmitting DTV antenna may differ greatly from the original signal that was sent by the DTV transmitter. The echoes may even cause the DTV signal and/or sound corresponding to a television program to be lost completely, and disrupt television service to a viewer. Testing devices are needed to analyze the performance of a DTV antenna transmitting system from the DTV transmitter to the transmitting antenna, and to provide data about the performance of the DTV antenna transmitting system, so that failures can be avoided. Methods exist for testing DTV transmitting systems that are capable of identifying whether or not echoes are occurring within a transmitting system. The conventional method of testing DTV transmitting systems requires going off-air and shutting down the DTV transmitting system, which can be costly, to connect the testing device to the transmission line. The conventional method of testing DTV transmitting systems utilizes a testing device, such as a network analyzer, that is connected to the transmission line via a connector/adapter. A low power test signal is then sent by the transmitter, and the network analyzer analyzes the signal received. The network analyzer is able to ascertain the magnitude of the problem (i.e., how much of the test signal was lost up to the point at which the network analyzer is connected) and the source or location of the signal loss. However, the network analyzer cannot be utilized to test DTV transmitting systems in real time while operating under full power. Additionally, the network analyzer is limited to a resolution of approximately a hundred feet if used with 6 MHz bandwidth, and thus unable to identify potential problems that are less than a hundred feet apart.

Another method of testing DTV antenna systems is described in U.S. Pat. No. 6,212,286 to Rott et al. (hereafter “Rott”) which discloses a method of testing a DTV antenna transmitting system in real time and under full power. Rott involves a method for testing an antenna system that enables the source/location of a problem to be identified by aiming an infrared camera at the component of the transmitting system to be tested while the component is in full operation.

The infrared camera records a thermal image of the test object. When the temperature of a portion of the thermal image is extremely high when compared to the remainder of the thermal image, the portion of the test object corresponding to the high temperature area on the thermal image is likely to be the source of the problem. Typically, a sharp increase in temperature is an indicator of a malfunctioning component. Thus, the area of the thermal image where there is a temperature increase can be matched to the area of the component that was tested.

The thermal image generated from the testing method of Rott reveals extreme temperature gradients. If an echo is created, that only causes a small increase in temperature, the echo may go undetected by the infrared camera of Rott. As a result, DTV service to consumers may be interrupted by the effects of the undetected echo signal.

Accordingly, it is desirable to provide a real time method for testing DTV antenna transmitting systems from the DTV transmitter to the DTV transmitting antenna that is operable under full power.

Further, it is desirable to provide a method for real time testing of DTV antenna transmitting systems that can identify the magnitude and the location of existing and/or potential problems.

Further, it is desirable to provide a method for testing a DTV antenna transmitting system that minimizes time and cost in identifying and resolving a problem that occurs within a DTV antenna transmitting system.

SUMMARY OF THE INVENTION

In one aspect of the present invention a real time apparatus for testing a DTV antenna transmitting system, where the DTV antenna transmitting system transmits an original signal from a DTV transmitter to a DTV transmitting antenna is provided that includes a probe, wherein the probe is connected in series with the DTV antenna transmitting system, and wherein the probe senses a signal traversing the DTV antenna transmitting system and generates a received signal, and an error detector which compares the received signal to the original signal to identify an error, wherein the error detector identifies the magnitude and location of the error, and a processor, wherein the processor compares the magnitude of the error to a predetermined value.

In another aspect of the present invention a real time apparatus for testing a DTV antenna transmitting system, where the DTV antenna transmitting system transmits an original signal from a DTV transmitter to a DTV transmitting antenna is provided that includes a means for sensing a signal traversing the DTV antenna transmitting system in real time and generating a received signal, and a means for comparing the received signal to the original signal to identify an error, and wherein the comparing means identifies the magnitude and location of the error.

In yet another aspect of the present invention, a method for testing a DTV antenna transmitting system, wherein the DTV antenna transmitting system transmits an original signal from a DTV transmitter to a DTV transmitting antenna is provided that includes sensing a signal traversing the DTV antenna transmitting system in real time and generating a received signal, and comparing the received signal to the original signal to identify an error, and identifying the magnitude and location of the error.

There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.

In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a block diagram of a system for testing, monitoring and/or optimizing an antenna system in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

Referring now to FIG. 1, a testing device 10 is provided for testing a DTV antenna transmitting system 12 in accordance with the present invention. In an exemplary embodiment of the present invention, the testing device 10 detects errors, such as those caused by echoes, in the DTV antenna transmitting system 12. The DTV antenna transmitting system includes a DTV transmitter 14, a transmission line 16 and a DTV transmitting antenna 18.

In an exemplary embodiment of the present invention, the testing device 10 includes a tuner 20, an echo/error detector 22, and an equalizer 24. A probe 26 and a processor/central processing unit (CPU) 28 are connected to the testing device 10 to provide for input and output of data from the testing device 10, while a display 30 and an input device 32 are connected to the processor 28.

The probe 26 is utilized to couple the testing device 10 to any point in the DTV antenna transmitting system 12. The probe 26 detects the signals that traverse the point in the DTV antenna transmitting system 12 to which the probe 26 is coupled. In exemplary embodiments of the present invention, the probe 26 is a voltage probe, current probe, single directional coupler or dual directional coupler. A directional coupler is a device that is utilized to sample a forward (incident) and/or backward (reflected) wave in a transmission line.

In an exemplary embodiment of the present invention, the probe 26 is connected in series with the DTV antenna transmitting system 12, such that the testing device 10 can monitor and/or test the signals traversing the DTV antenna transmitting system 12 continuously, at an instant point in time, and/or during discrete intervals in time. In an exemplary embodiment of the present invention the probe 26 and testing device 10 may be provided as part of the DTV antenna transmitting system 12.

In an exemplary embodiment of the present invention, the signal that is transmitted from the DTV transmitter 14 to the DTV transmitting antenna 18 is transmitted at a constant voltage level. The DTV signal is modulated at the DTV transmitter 14 by an eight-level VSB (8-VSB) standard, which is a modulation format that is utilized for the terrestrial transmission of DTV. The modulation format was established as the standard for DTV transmission in the United States by the Advanced Television Systems Committee (ATSC). The 8-VSB standard is considered an effective method for the transmission of DTV programming because it allows for either transmission of HDTV, or more than one standard DTV program (multicasting) and/or the transmission of other data along with a television program (data casting).

The tuner 20 is utilized to automatically or manually select a signal to be tested, monitored and/or optimized from the signals in the channel that are being transmitted from the DTV transmitter 14 to the DTV transmitting antenna 18 and sensed by the probe 26. In exemplary embodiments of the present invention, the tuner is utilized to demodulate the DTV signal.

The probe 26 senses the signals in the frequency domain, and outputs a waveform that indicates the magnitude of the signal of the signal as a function of frequency. In an exemplary embodiment of the present invention, the CPU 28 is coupled to the probe 26. The input device 32 is utilized to control the probe's level of sensitivity, i.e., the amount of the DTV signal that the probe is able to sense.

The recovered/received DTV signal that is sensed by the probe 26 may not correspond to the original signal that was transmitted by the DTV transmitter 14 if errors/echoes were generated during the transmission of the DTV signal from the DTV transmitter 14 to the DTV transmitting antenna 18. When echoes/error occur, the DTV signal will have varying signal levels, instead of one signal level.

The echo/error detector 22 is utilized to identify the occurrences of errors/echoes in the recovered signal by identifying where the DTV signal deviates from a constant level. The error detector 22 first identifies the baseband voltage by identifying the primary voltage from which the DTV signal is deviating. The levels of the recovered DTV signal is then compared to the identified baseband of the original DTV signal.

The error detector 22, generates an echo signal/error correction signal that corresponds to the differences between the baseband level of the original signal and the levels of the recovered signal. Accordingly, the amount of any “increases to” or “decreases from” the level of the original signal transmitted by the transmitter are attributed to echoes/errors, and the magnitude of the echoes/errors are known.

In an exemplary embodiment of the present invention, the display 30 is utilized to display the original signal, the recovered signal, and/or the echo/error correction signal. The display is also utilized to display the echo level versus distance. In exemplary embodiments of the present invention, the magnitude of the signal is expressed, for example, in decibels, as a voltage standing wave ratio (VSWR) and/or by a reflection coefficient.

Further, the location of the error/echo can be ascertained. The CPU 28 is utilized to determine the location of the error/echo along the transmission path from the DTV transmitter 14 to the DTV transmitting antenna 18. The CPU 28 is utilized to calculate the distance the echo is in air from, for example, the DTV transmitter 14, by utilizing the equation distance=speed time.

In an exemplary embodiment of the present invention, the distance is measured in feet or meters, the speed is 984 feet per microsecond or 299.9232 meters per micro second.

Accordingly, the location of the echo signal, relative to the DTV transmitter, can be identified by multiplying the speed of the signal by the time of the occurrence of the echo, which can be deduced from the echo signal generated. Thus, the distance can be easily calculated, and the magnitude of the echo signal can be displayed as a function of distance from a point in the DTV transmitting system 12.

In an exemplary embodiment of the present invention the CPU 28 is a processor that is utilized to convert the unit of measurements that will be utilized to display for example, the original signal, received signal, echo signal and or the echo signal level versus distance. The CPU 28 can be utilized, for example, to convert the magnitude of the signal level to decibels, a VSWR or a reflection coefficient.

In an exemplary embodiment of the present invention, the error/echo detector 22 is coupled to an equalizer 24. The equalizer 24 utilizes a 192-tap-decision feedback filter to generate a correction pixel that, if utilized, would reduce distortion in a signal caused by an echo/error.

The filter takes the coefficient weighted average of a finite number of source pixels (in this case 192), which are referred to as taps, to calculate the replacement/correction pixel for the pixel that is out of place because of the echo.

In an exemplary embodiment of the present invention, the filter samples/taps the DTV signal every ninety-three nano seconds. The error detector 22 of the present invention ascertains the magnitude and location of the echo signal by extracting the tap data, from the correction pixel data. The tap data corresponds to the energy of the echo signals. It should also be understood that other filters, which have a finite number of taps, may be utilized.

In an exemplary embodiment of the present invention, software is utilized, by for example, the CPU 28 to determine whether the echo/error signals are within an acceptable threshold. In another exemplary embodiment of the present invention, the software outputs an audible or visual alarm to alert a user of the test device 10 when the echoes/errors are at a level that threatens the performance of the DTV transmitting system 12.

In an exemplary embodiment of the present invention, the testing device 10 extracts the correction pixel data from the equalizer 24 and constructs or generates an echo/error correction signal that includes deviations, from the original signal of a constant voltage level, which correspond to the correction pixels. In an exemplary embodiment of the present invention, the equalizer 24 is an ATSC/8-VSB TV test receiver, either EPA models 50 or 53, by Rohde & Schwarz of München, Germany that has a resolution within forty-seven feet.

In an exemplary embodiment of the present invention, the tuner 20, error detector 22, and equalizer 24 are incorporated into the testing device 10.

It should be understood that the tuner 20, equalizer 24, probe 26, CPU 28, display 30, and input device 32 may exist separately from the error detector 22, either alone or in combination with another device.

It should also be understood that a testing device 10 in accordance with the present invention can also be utilized with other systems, for example, cellular systems, personal communications systems, and satellite systems.

By utilizing a testing device 10 in accordance with the present invention, which identifies the magnitude and location or errors/echoes in real time and under full power, a user of the testing device can identify errors/echoes that are of a magnitude that could interfere with the transmission of the DTV signal from the DTV transmitter 14 to the DTV transmitting antenna 18 without shutting down the DTV transmitting system. A user of the testing device 10 of the present invention can also adjust the components of the DTV transmitting system 12, which correspond to the location of where the error signal is occurring, to optimize the performance of the DTV transmitting system.

The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention. 

1. A method for testing a transmission line in real time during continuous application of a full-power digital television (DTV) transmission signal in the transmission line from a DTV transmitter to a DTV antenna, comprising: measuring a DTV transmission signal by extracting a continuous time-domain sample of the DTV transmission signal and converting the time-domain sample to the frequency domain; identifying an original frequency spectrum for the DTV transmission signal; and comparing the measured signal to the original frequency spectrum to detect errors in the measured signal.
 2. The method of claim 1, wherein the time-domain sample of the DTV transmission signal is extracted from a location along the transmission line.
 3. The method of claim 1, wherein the time-domain sample of the DTV transmission signal is extracted over a specified time interval.
 4. The method of claim 1, further comprising generating an echo signal/error correction signal that corresponds to the differences between the measured signal and the original frequency spectrum.
 5. The method of claim 4, wherein said generating the echo signal/error correction signal includes generating correction pixel data.
 6. The method of claim 5, wherein said generating correction pixel data includes generating tap data using a feedback filter.
 7. The method of claim 1, further comprising identifying as echoes differences between measured signal magnitudes and the original frequency spectrum.
 8. The method of claim 7, further comprising determining a location of an echo along a transmission path from a DTV transmitter to a DTV antenna.
 9. The method of claim 7, further comprising outputting an audible or visual alarm if the echoes exceed an error threshold.
 10. The method of claim 4, further comprising displaying at least one of the measured signal, the original frequency spectrum and the error correction signal.
 11. The method of claim 8, further comprising displaying echo magnitude versus distance. 